1. Field of the Invention
This invention relates to an apparatus for preparing a cultured food product, such as but not limited to tempeh, from a plant material.
2. Description of the Related Art
Tempeh has been a valuable and important food product which is traditionally prepared by fermenting and culturing whole dehulled soybeans or soybean grits or meal with cultures of beneficial fungi or microorganisms. Although tempeh is made from soy, it has a unique taste and is mildly flavorful on its own, unlike tofu, and also has different nutritional characteristics and textual qualities. Tempeh's fermentation process and its retention of the whole bean give it a higher content of protein, dietary fiber, and vitamins. It has a firm texture and an earthy flavor which becomes more pronounced as the tempeh ages. Because of its nutritional value, tempeh is used worldwide in vegetarian cuisine; some consider it to be a meat analogue.
Tempeh has traditionally been prepared by first soaking whole soybeans in water. The soaked, wet soybeans are then dehulled and boiled in water to soften the beans and destroy any contaminating microorganisms. The cooked soybeans are then spread out in thin layers to allow the water to drain and evaporate from the surface of the soybeans. The air dried soybeans are then mixed with a starter comprising portions of old tempeh containing a mixture of molds, bacterial and other microorganisms. The moist inoculated soybeans are then wrapped tightly and the material is allowed to culture at room temperature until the soybeans are completely molded. This product is known as tempeh, which can be eaten as is or sliced into thin slices, dipped into a salt solution and fried in a vegetable oil. Currently, tempeh can be made by soaking the beans or legumes and then boiling them until soft and anti-nutritional components have been eliminated or diminished. They are then dried off and sliced in a vegetable slicer (with skins). Then the tempeh starter culture is added and mixed into the substrate, after which it is ready for incubation. Commonly, tempeh is pasteurized after incubation.
The culturing of soybeans destroys the bad odor and bad flavor of soybeans by causing the microorganisms to produce enzymes that act on the proteins, carbohydrates and the oil in the soybeans to make the tempeh palatable and nutritious and to give a desirable flavor. Examples of microorganisms used in tempeh culturing are Rhizopus oryzae and Aspergillus oryzae; most often: Rhizopus Oligosporus. These microorganisms require aeration for growth and the formation of enzymes. During the culturing process, the soybeans must be spread out in layers that are relatively shallow in depth, due to the microorganisms used in making tempeh being aerobic. Resultantly, this means that the area of the soybean layers must be large.
The use of large area trays is common for commercial production of tempeh. Martinelli and Hesseltine (1964) Food Technology, Vol. 18, No. 5 found that large metal trays were excellent for commercial tempeh production because they were more sanitary and allowed for easier removal of the tempeh from the container in comparison to wooden trays (unless the wooden trays were lined with perforated plastic sheeting). The metal trays were reported to be preferably large aluminum trays instead of large stainless steel trays. However, the use of aluminum in prolonged contact with food is being questioned in relation to its possible implication in causing diseases, such as Alzheimers. Stainless steel is not a very good heat conductor and has less than 10 percent of the thermal conductivity of aluminum. In some instances, using stainless steel can result in a build-up of heat at the center of the tray which can cause spoilage of the tempeh in the area around the center of the tray.
A common practice in the preparation of tempeh is to cover the soybean layer with a film. The use of banana leaves in place of the film is a traditional method but can cause contamination, and the banana leaves are not reusable. Other films that can be used are polyethylene film or wax paper.
A common method of making tempeh consists of incubating a layer of soybeans covered with a flexible plastic sheet modified with aeration perforations. The incubation process takes place in an incubation room having an agitated airflow that is uniformly heated or cooled and with a consistent humidity. A disadvantage with the common method is that agitation of the airflow often leads to blackened areas on the tempeh where the airflow meets the microorganisms at the perforated holes. This contact with the fast moving airflow causes the microorganisms to sporulate prematurely and produces undesirable black spores. The greater the agitation of the airflow to ensure that the air in the incubation room does not stratify, the greater the occurrences of premature sporulation. Furthermore, it can be difficult to accurately control the humidity in the incubation rooms. If the airflow is slightly drier than optimum, the black spore problem is increased.
U.S. Pat. No. 3,228,773 to Hesseltine et al describes a method of preparing tempeh by fermenting soybeans with certain phycomycetous fungi of the order Mucorales, genus Rhizopus. The soybeans are soaked overnight, the seed coats are removed and the whole soybeans may be cracked into large grits. The soybeans are then softened and moistened by soaking in water and then boiled to sterilize and further soften the soybeans. Excess water is drained and the soybeans are cooled below 104° F. (40° C.) and then inoculated with a spore suspension of Rhizopus spores. The soybeans are cultured in conventional non-toxic plastic bags modified by the presence of 0.02 inch diameter perforations located not over 0.5 inches apart. The soybeans are also described as being cultured in perforated flexible, plastic tubing having a diameter of 3.5 inches (9 cm). In either example, the resulting tempeh must be removed from the plastic container and then cooked to prepare the tempeh as a consumable food.
U.S. Pat. No. 5,228,396 to Pfaff describes an apparatus for culturing plant materials as food, such as tempeh, wherein the apparatus comprises at least a container, such as a stainless steel tray, holding a plant material partially immersed in a water bath, and a cover covering the container. A heater heats the water bath such that the water bath evenly distributes the heat to the container, thereby allowing the plant material to be uniformly cultured. Regulation of the temperature of the water bath is done by increasing the heat of the heater or by adding cold water to the water bath.